1. Field of the Invention
The present invention relates to a mobile communication system and a switching apparatus in the mobile communication system, in which the mobile communication system includes a plurality of base stations, a control station which controls the base stations and switching apparatuses each of which corresponds to the base station or the control station and switches a communication partner.
2. Description of the Related Art
FIG. 1 shows an example of a conventional mobile communication system. The mobile communication system shown in this figure includes three wireless base stations 3-1–3—3 and a control station 4 which controls the wireless base stations 3-1–3—3. In this mobile communication system, the wireless base stations are connected each other by using switching apparatuses 5-1–5-3 and wireless circuits 20 or an optical fiber circuit 30, and each wireless base station and the control station 4 are connected by using switching apparatuses 5-1–5-4 and the wireless circuits 20 or the optical fiber circuit 30, in which the switching apparatuses 5-1–5-3 are provided for the wireless base stations 3-1–3—3, and the switching apparatus 5-4 is provided for the control station 4.
For example, when a mobile terminal 1—1 sends a signal, the signal is received by the wireless base station 3-1, via an antenna 7-1, wherein the mobile terminal 1—1 is included in a cell 2-1 of the wireless base station 3-1. The signal received by the wireless base station 3-1 is received by a radio transceiver unit (RTRU) 21-1, 21-2 or an optical transceiver unit (OTRU) 31-1 by a switching operation of the switch 11-1 in the switching apparatus 5-1 according to the destination of the signal. Then, the signal is transmitted to another wireless base station 3-2 or 3—3, or to the control station 4 via the RTRU 21-1 or 21-2 and the wireless circuit 20, or via the OTRU 31-1 and the optical fiber circuit 30.
The RTRU in each of the switching apparatuses 5-1–5-4 includes a wireless modem 23 and a wireless transceiver (TR) 24, which are not shown in the RTRUs 21-1–21-6 in the switching apparatuses 5-1–5-3 of the wireless base stations 3-1–3—3 in FIG. 1. A signal which is received by the RTRU 21-1 is converted into a signal having a transmission form for wireless transmission by the wireless modem, and transmitted to the wireless circuit 20 via the antenna 22-1 by the wireless transceiver.
Each of the OTRUs 31-1–31-4 in the switching apparatuses 5-1–5-4 includes a signal converter 32 and an optical transceiver (E/C, O/E) 33, wherein the signal converter 32 and the optical transceiver 33 are not shown in the OTRUs 31-1–31-3 in the switching apparatuses 5-1–5-3 corresponding to the wireless base stations 3-1–3—3 in FIG. 1. For example, a signal input into the OTRU 31-1 is converted into a signal having a transmission form for optical transmission and the signal is transmitted to the optical fiber circuit 30 by the optical transceiver.
When receiving a signal, the operation of the wireless base station 3-2, 3—3 or the control station 4 is as follows. When the control station 4 receives the signal, a signal transmitted from the wireless base station at the sending side via the wireless circuit 20 or the optical fiber circuit 30 is received by the RTRU 21-7, 21-8 or the OTRU 31-4 in the switching apparatus 5-4 of the control station 4. Then, the signal is sent to a multiplexer/demultiplexer part 42 by a switching operation of the switch 11-4, and is sent to a mobile communication network via a circuit control apparatus 43.
When the receiving side is the wireless base station 3-2, a signal sent from the wireless base station 3-1 in the sending side via the optical fiber circuit 30 is received by the OTRU 31-2 in the switching apparatus 5-2, and the signal is sent to a mobile terminal 1-2 via an antenna 7-2 by a switching operation of the switch 11-2. In addition, when the receiving side is the wireless base station 3—3, a signal transmitted to the wireless circuit 20 from the wireless base station 3-1 is received by the RTRU 21-5 in the switching apparatus 5-3, and the signal is sent to the mobile terminal 1-3 via the antenna 7-3 by a switching operation of the switch 11-3.
However, since the wireless base stations or each wireless base station and the control station are connected by the wireless circuit 20 or the optical fiber circuit 30, the transmission medium is different according to the destination of the signal. Therefore, the switching apparatus 5 needs to convert a signal into a signal suitable for transmission medium. Thus, there is a problem in that sharability in the apparatus is low. Therefore, it is necessary to add or change the RTRU or the OTRU in the conventional switching apparatus when a transmission medium is added or changed. As a result, it is difficult to construct a network.